Sales of women’s clothing, a traditional pillar of the holiday shopping season, are unusually weak so far this year, according to a major credit card company, an ominous sign for the retail industry.

From high-end dresses to bargain coats, spending on women’s apparel dropped nearly 6 percent during the first half of the Christmas season, compared with the same period last year, according to MasterCard Advisors, a division of the credit card company.